The present invention relates to propeller brakes and methods for braking propellers and propeller shafts.
It is often desirable to stop the propeller of a turbo-prop engine for various reasons. For example, a propeller can be stopped in the event of an engine failure. Also a pilot may stop the propellers of a commercial turbo-prop powered aircraft when passengers are boarding or leaving the aircraft, by stopping the engine. However, the resulting thermal cycling of the engine occasioned by the frequent starting and stopping of the engine appreciably reduces engine life. Stopping the engine also requires the use of an auxiliary power unit to provide essential electrical and hydraulic services to the aircraft during the period when the engine or engines are shut down.
From an efficiency point of view, it is desirable to keep engines running while the passengers are boarding or disembarking from an aircraft. However, rotating propellers are highly dangerous to unwary passengers and crew members in the vicinity of the aircraft. Additionally, even in a feathered state, whirling propellers produce objectional wind gusts.
It is known to employ brakes to stop a propeller in the event of an engine failure. These known brakes employ various reciprocating parts such as frustroconical brake drums to frictionally resist shaft rotation. Some propeller brakes employ a plurality of angularly spaced brake shoes. Also known are couplers using helical splines that can disengage the drive to a propeller when torques reach a value indicating that the propeller may be windmilling or that the engine may have failed. Examples of such propeller brakes are disclosed in U.S. Pat. No. 2,141,091; 2,737,018; and 3,225,876.
An important requirement for a propeller brake for large aircraft is high braking power to allow rapid stopping of a relatively large propeller rotating at high angular speed. A disadvantage with known propeller brakes is they ordinarily employ a single, relatively small braking surface. Consequently, these brakes can be easily overloaded or can only stop a propeller after an unacceptably long braking period.
Another important design consideration for propeller brakes is that they fail safe and do not inadvertently brake a propeller during flight or inadvertently release a propeller when its rotation could be dangerous.
Accordingly, there is a need for a compact, efficient and safe propeller brake having high braking power.